1. Field of the Invention
The present invention relates to an ink jet recording medium having a coating for absorbing aqueous dye-based inks. The coating comprises a blend of cellulose ether(s) and stilbene optical brightener(s).
2. Brief Description of the Related Art
The present invention relates to coated ink jet recording media, such as papers and films, which can be color imaged with aqueous dye-based inks from ink jet printers. By "aqueous dye-based inks` as used herein, it is meant ink compositions containing a water-soluble dye, wherein the solvent or carrier liquid is primarily water. In addition to water and dyes, the ink may contain pigments, organic solvents, humectants, detergents, thickeners, preservatives, and the like. The ink jet recording media of this invention are coated with an ink absorbent composition. By an "ink absorbent composition or coating" as used herein, it is meant a composition or coating which absorbs aqueous-dye based inks.
In order to provide high quality color images, ink jet recording media are typically coated with an ink absorbent composition. During imaging or printing with ink jet printers, the ink absorbent coating absorbs the aqueous dye-based ink quickly so that the ink can dry quickly. Ink absorbent (or ink receptive) coatings are known in the art and typically comprise a hydrophilic polymeric material that is soluble in water and swells upon exposure to water. Suitable hydrophilic polymeric materials include, for example, poly(vinyl alcohol), cellulose ethers, cellulose esters, poly(vinyl pyrrolidone), gelatins, poly(vinyl acetate), starch, poly(acrylic acids), poly(ethylene oxide), proteins, hydroxypropyl cyclodextrin, poly(2-ethyl-2-oxazoline), alginates, water-soluble gums, and the like.
It is sometimes desirable to add certain optical brighteners to certain polymeric coatings on ink jet recording media in order to brighten the coatings.
For example, Nikoloff, U.S. Pat. No. 5,660,622 discloses a coating composition for ink jet recording sheets. The composition contains a mixture of hydrated amorphous synthetic silica, synthetic binder, cationic agent, leveling-flow modifier, dispersing agent, optical brightener, and water. In addition, the patent states that the coating may also include titanium dioxide pigment and/or a viscosity modifier. The patent discloses that the water-dispersible synthetic binder may be an acrylic prepolymer or polyvinyl alcohol (PVA), and the viscosity modifier may be alginates, carboxyl methyl cellulose, hydroxyl methyl cellulose, or polyacrylates. The patent states that the preferred optical brightener material includes a stilbene yellow base and is preferably in the coating composition at a weight percent range of 0.2 to 2%.
Cahill et al., U.S. Pat. No. 5,766,398 and Brault et al., U.S. Pat. No. 5,795,425 disclose processes for making protected, distortion-free, full-color ink jet images for use on large format posters, billboards, and the like. The patents disclose that the ink receptive layer on the receptor element may be prepared from a variety of hydrophilic aqueous ink absorptive coating materials. In addition to the polymeric or resin components, the patents disclose that the ink receptive layer typically contains other added components such as a dye mordant, a surfactant, particulate material, a colorant, ultraviolet absorbing materials, organic acids, an optical brightener, and the like. The patent discloses that optical brighteners which may be used to enhance the visual appearance of the imaged layer may be any conventional, compatible optical brightener, e.g., optical brighteners marketed by Ciba-Geigy under the trademark of Tinopal.RTM..
One particular problem with ink jet recording media coated with compositions containing cellulose ethers is that the media exhibit undesirable color shifts after the media have been imaged with a color image. By "color shifts", it is meant that the color of the image changes over time. These color shifts are most noticeable on ink jet recording media having a magenta-colored image. When magenta ink is used to form the image, the image is initially a magenta (deep purplish red) color, but it often fades and appears hot pinkish over a relatively short period of time. It would be desirable to have ink jet recording media, where such magenta color shifts are minimized or eliminated. The present invention provides such ink jet recording media.